US3872455A - Physiological measurement display system - Google Patents

Abstract

A system for receiving and displaying data generated by a transmitter having an output pulse rate corresponding to a measured parameter is disclosed. A portable receiver is provided which includes means for detecting weak signals having a repetitive burst rate, means for locking onto the burst rate and producing a corresponding train of pulses, means for counting the number of pulses received during a predetermined time period and means for displaying a number related to the received pulse rate to provide a digital representation of the monitored parameter. The system further includes means for compensating for nonlinearities in the pulse rate of the received signals due to known non-linearities in the signal generator, and includes means for disabling the display in the event of an incomplete measurement, whereby accuracy of the display is assured. The receiver is particularly useful in combination with a physiological sensor-transmitter which produces signals having a pulse rate related to a measured parameter, such as temperature.

Description

United States Patent 1191 Fuller et a1.

[ PHYSIOLOGICAL MEASUREMENT DISPLAY SYSTEM [75] Inventors: Charles H. Fuller, Carson; Carl E.

Herring, Huntington Beach, both of Calif.

[73] Assignee: Monitron Industries, Inc.,

Huntington Beach, Calif.

[22] Filed: Nov. 13, 1972 [21] Appl. No.: 306,253

Related US Application Data [63] Continuation-impart of Ser. Nos. 199,675, Nov. 17, 1971, and Ser. No. 200,368, Nov. 18', 1971, and Ser. No. 199,847, Nov. 18, 1971, and Scr. No. 199,979, Nov. 18,1971.

[52] U.S. Cl...... 340/189 M, 340/177 VA, 340/178, 340/206, 340/207, 128/21 A, 343/842 [51] Int. Cl G08c 19/26 [58] Field ofSearch 340/347 AD, 206, 207;

l28/2.1 A; 73/362 AR; 325/113; 324/78 D; 343/842 [56] References Cited UNITED STATES PATENTS 2,394,787 2/1946 Kreager 343/842 2,990,541 6/1961 Gill 340/206 3,453,546 7/1969 Fryer 325/118 3,495,264 2/1970 Spears 343/842 /0 l2 .3. l l /6 8 l I l 1 20 I BLOCKING SENSOR 05c. 3

[ Mar. 18, 1975 3,534,728 10/1970 Barrows 73/362 AR 3,572,316 3/1971 Vogelman m1. 340/207R 3,656,132

4/1972 Brumbelow 340/195 Primary ExaminerThomas B. Habecker Attorney, Agent, or' Firm-Jones, Tullar & Cooper [57] ABSTRACT A system for receiving and displaying data generated by a transmitter having an output pulse rate corresponding to a measured parameter is disclosed. A portable receiver is provided which includes means for detecting weak signals having a repetitive burst rate, means for locking onto the burst rate and producing a corresponding train of pulses, means for counting the number of pulses received during a predetermined time period and means for displaying a number related to the received pulse rate to provide a digital representation of the monitored parameter. The system further includes means for compensating for nonlinearities in the pulse rate of the received signals due to known non-linearities in the signal generator, and includes means for disabling the display in the event of an incomplete measurement, whereby accuracy of the display is assured. The receiver is particularly useful in combination with a physiological sensor-transmitter which produces signalshaving a pulse rate related to a measured parameter, such as temperature.

42 Claims, 23 Drawing Figures /4 L I RF AMF? PHASE I DEMODULATOR SWEEP AND AND 1 PULSE SHAPER LO CK DISPLAY.

PATENTED 3,872,455

SHEET Cl 0F 16 l0 /2 l4 L I l6 /8 I 22 RFAMF! PHASE I SENSOR BLOlgclNG I I DEMODULATOR- SWEEP N AND I I PuLs SEIAPERLOCK L 2 4 39 v 2a i DISPLAY Loenc PATENTEDHAR I 81975 saw 03 or 16 VCO NOR

COUNTER lllllllllll'l l.

COUNTER COUNTER PATENTEB AR 1 81575 3.872.455sum GBUF 16 PATENIEUHAR] 8 I975 SHEET CS'GF 16 lOlO COU NT SWEEP GEN (390) LOCK ON 0 RESET (40o).

Locmasai LOGIC 0y RECEIVER OUTPUT (384) LOCAL OUTPUT TO DISPLAY COUNTER BLANK CLOC K (408) CURVE SHAPING POWER ON PATENTEDHAR] 8 I975SHEET 10 0F 16 PAIENT MAM 81975SHEET llUF 16 Nmym MGM

mam v.06 |l 20 E E0 W E mokuwhwo vbm mKm

PATENTEI] MAR l 8 I975sum lh UF 16 PHYSIOLOGICAL MEASUREMENT DISPLAY SYSTEM CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of the following U.S. Pat. applications copending with the present application, but now abandoned: Ser. No. 199,675, of Charles H. Fuller, filed Nov. 17, 1971, for a Physiological Testing System; Ser. No. 200,368 of Carl E. Herring, filed Nov. 18, 1971, for a Measuring and Display System; Ser. No. 199,847 of Charles H. Fuller, filed Nov. 18, 1971, for a Physiological Transmitter; and Ser. No. 199,979 of Charles H. Fuller, filed Nov. 18, 1971 and entitled Bio-Medical Transmitter. The present application ia also related to the continuationin-part application of Ser. No. 199,847 and Ser. No. 199,979 of Charles H. Fuller, which application was filed on even date herewith has been assigned Ser. No. 306,097, and is entitled Physiological Sensor and Transmitter.

BACKGROUND OF THE INVENTION data has become a highly developed art in recent years,

and many systems have been designed for this purpose. Such systems have included sensors of various types which are secured to a patient to detect various phenomena and which produce electrical signals carried by means of electrical leads to suitable measuring and display equipment. However, for many purposes the requirement for a cable connection between a measuring or display device and a sensor secured to a patient is undesirable, for it is uncomfortable and substantially restricts his freedom of movement. Accordingly, telemetry systems have been developed which utilize a small,

self-contained transmitter in combination with the sensor, the unit being used to transmit the sensed data to a remote receiver. Such systems are described, for example, in the applications related to the present application, identified above, all of which are assigned to the assignee of the present case. Typically, in such systems the transmitters utilize a suitable blocking oscillator which has a resonant circuit, the inductor of which serves the dual function of tuning the oscillator and generating a radio frequency field which may be detected by a receiver system. As disclosed in the afore mentioned related applications, the blocking oscillator is modulated by a sensor to emit bursts or pulses of radio frequency energy at a rate that corresponds to the magnitude or other characteristic of the parameter being monitored.

The physiological parameter to be measured may be the temperature, blood pressure, cardiac (ECG) voltage, or other condition of a human patient. Where, for example, the temperature of a patient undergoing medical observation is to be monitored, a sensing element such as a thermistor is employed to sense the temperature and to vary the output pulse rate in accordance with the monitored value. It will be apparent, however, that such a monitoring-transmitting system will have many applications outside the medical field.

ln order to utilize a wireless system for measurement of physiological parameters, great care must be taken in designing both the transmitter and the receiver to insure a high degree of accuracy both in the transmission and in the reception and display of the monitored data, for the results of such measurements may often be critical tothe health andsafety of the patient. Accordingly, the design of both the transmitter and the receiverdisplay unit must take into account the numerous factors which can affect such measurements. In the prior art, attempts to do this have led to exceedingly complex systems which are not only expensive, but because of their complexity are not entirely reliable. Further, where the transmitter and receiver are not carefully matched, inaccuracies can arise due to differences in the response characteristics of the two units, making them unsatisfactory. In addition, in any practical use of the system, it will be desirable to employ a single receiver in combination with any one of ,a plurality of transmitters so that, for example, a sensor-transmitter can be placed on a number of patients on adjacent beds in a single room, and the receiver can be utilized to provide a display of the temperature of one and then another, without interference, and with a high degree of accuracy.

Prior receivers for such systems have suffered prob lems of instability due not only to interference from outside sources, but from jitter of the received pulses and from an inability to respond to weak signals. Such systems will often respond to harmonics of the desired signals rather than, or in addition to, the desired signals, thus producing inaccurate readings. 1n addition, many receiving units have local radio frequency oscillators in an attempt to improve their response to transmitted signals, but such units have instead compounded the problem by producing their own radio interference. Occasionally, prior systems would respond to a partial signal that would produce a partial and thus inaccurate reading, which, if not recognized by the operator, could result in an injury to the patient.

Finally, the complexity and thus the high cost of prior devices, together, with their inadequacies as to operation, have seriously detracted from the commercial application of such systems. Attempts to overcome these difficulties have led to designs in which the response of the receiver is relatively slow, and the delays produced in such units together with their inaccuracies and unreliability have made them unsatisfactory to potential users.

SUMMARY OF THE INVENTION vide a receiver for a physiological telemetry system which is capable of receiving a pulse frequency modulated signal from a sensor-transmitter, and displaying accurately, and in a relatively short time, the information so received.

It is another object of the present invention to produce a receiver which is capable of detecting a pulse modulated signal in the presence of noise and rapidly and accurately providing a display of the sensed signal data.

It is a further object of the present invention to provide a receiver which is capable of producing a readout display of a received data and which compensates for nonlinearity in the characteristics of the transmitter.

It is a further object of the present invention to provide a small, portable, easy to use, and reliable receiver for displaying a numerical representation of a monitored parameter.

It is another object of the present invention to provide a small portable, battery-operated receiver which will obtain accurate readings over a short period of time, without resorting to complex coding systems, will provide a stable response to weak signals and in the presence of interference, and will prevent the display of an inaccurate readout in the event of an incomplete measurement.

It is a further object of the invention to provide a method of detecting a physiological parameter ofa subject by locating a sensing element on the patient, developing in a transmitter winding bursts of magnetic field energy at a burst rate corresponding to value of the parameter, receiving the bursts of magnetic field energy,

' and measuring the frequency at which the bursts occurto provide an indication of the value of the physiological parameter.

These and other objects of the invention are accomplished through the provision of a sensor-transmitter which is mounted in a small compact housing which may be removeably secured to a patient as by means of a double-faced adhesive sheet. The housing for the sensor-transmitter is constructed of a molded plastic which is formed to provide a specific chamber for each component of the transmitter circuitry to assure that the various components are correctly located for optimum operation of the device. The components are so arranged that the normal component leads may be used to provide the required interconnection between the elements, providing speed and reliability of assembly. The battery supply for the unit is located within the transmitter antenna winding and is accessible by way of an opening in the housing to permit battery replacement. The sensor device is secured to the exterior of the housing and connected to appropriate leads which extend through openings in the housing. Also extending through openings in the housing are a pair of switch leads which are mechanically separated to hold the circuit in an inoperative condition to assure a long shelflife for the unit. A switch cover is provided to mechanically interconnect the switch leads to activate the device, the switch cover snapping into place to provide a substantially permanent activation of the unit which lasts until the battery must be replaced.

The transmitter circuitry comprises a blocking oscillator which is capable of producing bursts of radio frequency energy, with the bursts being repetitive at a rate determined by the sensor unit. In a preferred embodiment, this sensor is a thermistor adapted to measure the temperature of a patient, although other forms of sensor may be used equally well. These bursts of radio frequency energy are generated'in a resonant tank circuit which includes an inductor, the windings of the inductor also acting as the antenna for the transmitter device.

While the term transmitter is used in describing this invention, it will be understood that the term does not necessarily imply the transmission of waves by a wellknown radio techniques to a remote receiver miles away. Radio frequency signals that are transmitted by an ordinary radio antenna system may, of course, be detected by a receiver located in a far-field region, but such signals may also be detected in a near field region, or area. The boundary between the tworegions is generally considered to be located a distance of approximately seven wave lengths from the transmitter antenna. The energy emitted from the antenna and attributable to these two fields is characterized by different fall-off rates or by different relations between the alternating magnetic components and the alternating electrical components of the field. For example, in a farfield area, the electric and magnetic field strengths are proportional to each other and the amplitude of each falls off inversely with the distance. Within the nearfield area neither of these relations exists. The alternating electric and magnetic fields in the near area are not proportional to each other, nor are they in the same phase relationship. This near field" is often known as the induction field. These effects are discussed briefly in Radio Engineers Handbook." by Frederick Emmons Terman (McGraw Hill, 1943). it is to be noted that the electric induction field and the magnetic induction field in the near field fall off at rates which vary inversely as a low power of distance; for example, they vary inversely as the distance or as the square or as the cube thereof.

This invention is primarily useful in an even closer range, called the extreme near field region; in this region the transmission of energy from the transmitter to the receiver occurs by magnetic induction, and the action is in the nature of that of a loosely-coupled transformer. However, the'primary winding and secondary windings are not wound on a common core, and the transmitter and receiver form separate units that may be moved about independently of each other. In other words, the relation between the transmitter and receiver is of the wireless type. In the best embodiment of this invention, the antenna is in theform ofa primary winding that encircles a tubular soft ferromagnetic core in the shape of a hollow cylinder with open ends, and the receiver employs an antenna in the form of a secondary winding of similar construction. With such a transformer, the strength of the induced field falls off at a much more rapid rate than either the far field or the near field ordinarily under consideration in a radio transmission system. Although such a field characteristic is ordinarily undesirable in a telemetry system for bio-medical purposes, where a condition of a patient is being observed the requirements of accuracy and reliability are paramount, and thus the present invention inches, and 52 inches, respectively, in the same direction from the transmitter. This represents a fall-off rate corresponding to a power of about 2.75 of the distance. That is, the detected voltage varied inversely as the 2.75 power of the distance from the center of the transmitter. These signals were measured in the equatorial plane of the transmitter i.e., in the plane normal to the axis of the transmitter coil.

The region in which the detectible radio frequency energy falls off in such a rapid manner may be referred to as the extreme near field region. The outer boundary of the extreme near field region, though not precisely defined, is referred to as its minimum useful range or the transitional coupling region. The range of this extreme near region is only one or two meters, being only a small fraction, such as 1% or 2% of the wave length.

In the specific embodiment of this invention described in detail below, the wave length of the radio frequency carrier wave is 70 meters, and the measurements are made with the receiver located 2 meters or less from the transmitter.

It will be understood that the far-field component,

component predominates, beyond that range and up to about seven wave lengths the so-called near field component predominates, and beyond about seven wave lengths the far field component predominates. Although the transmitter in its best mode of practice is particularly suitable for use only in the extreme near field transformer action region, in some of its forms it is useful in other regions.

The receiver is a high gain unit that is tuned to pick up the pulses generated by the transmitter and to convert them into square wave audio frequency signals having a frequency corresponding to the burst rate of the transmitted signals. These square wave signals are fed to a locking circuit, which produces a pulse train having a repetition rate equal to that of the average rate of the transmitted signals, and which eliminates the effects of pulse rate jitter, transients, harmonics, and the like. As soon as a lock-on condition occurs, the locking circuit feeds its pulse train output into a converter logic circuit. This logic circuit includes a very stable clock oscillator which operates at a preselected rate to feed a preset number of pulses (e.g. 632) to a display counter. The logic then produces a short delay, after which an additional number of pulses from the locking circuit pulse train are also fed to the display counter. The pulse train is fed to the display counter during a predetermined time period, with the exact number of pulses reaching the display counter being dependent upon the rate of the received signals, and thus upon the parameter being measured. The sum of these two pulse counts is then displayed to provide a numerical readout which corresponds to the sensed parameter.

Since the frequency output of the transmitter is not linear with a given change in the measured parameter,

a digital feedback is provided in the time base circuit of the receiver logic to correct for this non-linearity.

The receiver unit is a small hand-held unit having a display face on which are located four incandescent numerical display tubes, each having seven segments for displaying the numbers zero through 9. A display push button is provided on the receiver and when the unit is within the range of a transmitter, the button may be depressed to start the measuring and display operation. The received signals are counted, and at the completion of the count the display is unblanked and latched to producea display of the received count which will be held until the push botton is released. With the present improved system, an indication of the received data is provided within 0.4 seconds. If the count is not acquired by the receiver system for some reason, the push button must be depressed again to obtain the desired reading.

The display lamps are continuously biased on by a small current so that the incandescent filaments will be energized just below the visible level, thereby permitting a-faster and brighter display when a reading is acquired. If desired, the display of the receiver unit may also be used to provide a time multiplex output for recording purposes or for computer input.

The receiver unit is battery powered, with a full charge permitting over 1200 readings at two seconds each or a single reading for 45 minutes. The batteries are rechargable, and for this purpose a charging stand is provided on which thereceiver unit may be placed during periods of non-use. With a regular recharging,

' a single receiver unit may be used to monitor approximately 400 patients, obtaining four readings in every 24 hours, on a continuous basis.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and additional objects, features, and advantages of the present invention will become evident to those skilled in the art upon a reading of the following detailed description thereof, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of a transmitter and receiver system embodying the present invention;

FIG. 2 is a schematic diagram of atransmitter circuit useful with the sensor-transmitting unit of the system of FIG. 3 is a partial perspective view of an antenna winding suitable for use with the transmitter unit of FIG. 1;

FIG. 4 is a perspective view of an antenna suitable for use with the receiver unit of FIG. 1;

FIG. 5 is a cross-sectional view taken along lines 55 of FIG. 4;

FIG. 6 is a schematic diagram of a demodulator and pulse shaper circuit for use with the receiver unit of FIG. 1;

FIG. 7 is a block diagram of a phase sweep and lock circuit suitable for use in the receiver of FIG. 1',

FIG. 8 is a block diagram of a first embodiment of a logic and display system suitable for use in the receiver of FIG. 1;

FIG. 9 is a block diagram of the lock-on counter unit of FIG. 8; I

FIG. 10 is a block diagram of a second embodiment of a logic and display unit for use in the receiver of FIG.

FIG. 11 is a block diagram of a third embodiment of a logic and display unit for use in the receiver of FIG. 1.

FIG. 12 is a graphical illustration of the temperature vs. frequency characteristic of the transmitter;

FIG. 13 is a block diagram of an improved receiver, logic and display circuit for use in the system of FIG.

Claims (42)

1. A system for transmitting and receiving signals corresponding to a physiological parameter of a subject, comprising: a sensing element adapted to detect a desired physiological parameter of the subject; a transmitter adapted to transmit radio frequency signals modulated in accordance with signals that correspond to the detected physiological parameter, and a receiver unit adapted to inductively receive said transmitted signals, said receiver unit including demodulator means for producing a train of pulses at a frequency corresponding to the frequency of modulation of said radio frequency siganls; phase lock circuit means adapted to generate a range of frequencies that overlaps said frequency of modulation, said phase lock circuit means being connected to receive and compare the pulses developed at the output of said demodulator with said range of frequencies, whereby said phase lock circuit means locks onto, and thereafter generates output pulses at a rate corresponding to, said frequency of modulation; and means responsive to said output pulses for measuring the burst rate of the received radio frequency signals to indicate the magnitude of said physiological parameter.

2. The system of claim 1, wherein said means responsive to said output pulses comprises: a timer unit including a clock-pulse source, a timer counter, and means for feeding clock pulses from said clock pulse source to said timer counter; means for producing a first predetermined number of auxiliary pulses during a first timer interval; means controlled by said timer unit for gating said output pulses during a second timer interval; accumulator means; and means controlled by said gated pulses and by said auxiliary pulses for storing in said accumulator means a manifestation of a total-number representing the value of said parameter.

3. The system of claim 2, further including a device for displaying numbers in visible form, and means controlled by said accumulator means for operating said device to display invisible form numbers corresponding to the total number of pulses in said accumulator means.

4. The system of claim 2, further including means for modifying said second time interval to compensate for nonlinearities in the output characteristic of said transmitter.

5. The system of claim 4 wherein said means for modifying said second time interval comprises scanning means for feeding to said timer counter both said clock pulses and said output pulses to increase the counting rate of said timer counter.

6. The system of claim 5, further including gate means for preventing said output pulses from reaching said summing means during a predetermined portion of said second time interval.

7. A telemetering system for monitoring a physiological parameter of a plurality of spaced apart patients respectively, comprising: a separate telemetering transmitter mounted on each of the different patients, each of said transmitters comprising a blocking oscillator adapted to generate carrier waves of about the same radio frequency at a burst rate that corresponds to the physiological condition of the patient on which said each transmitter is mounted, and a single telemetering receiver for receiving signals at the aforesaid radio frequencies, said receiver including a. a demodulator having a pulse-amplitude discrimination circuit whereby the strongest of the signals received from said transmitters are detected and signals from other transmitters are suppressed, and b. means responsive to the output of said demodulator for measuring the burst rate of the received signals to indicate the physiological parameter of the patient on which the corresponding transmitter is mounted without interference from signals of any other of said transmitters.

8. The telemetering system of claim 7, wherein said means for measuring the burst rate of said received signals comprises: an accumulator for storing a total-number in digital form; auxiliary means for producing a set of digital signals that are at least partially dependent on the value of said parameter at a zero burst rate; a timer unit, including a clock pulse source, and a timer counter; starter means for initiating operation of output counter, said timer unit, and said auxiliary means; means controlled by said starter means for feeding pulses from said clock pulse source to said timer counter whereby a timing operation is initiated; means controlled by said starter means for feeding said set of digital pulses to said accumulator; means controlled by said timer unit for feeding pulses corresponding to said burst rate to said accumulator; and means controlled by said timer unit when the number of clock pulses fed to the timer counter has reached a predetErmined count for discontinuing the feeding of further pulses to said accumulator.

9. The telemetering system of claim 8, further including means for modifying said timer unit whereby the time elapsed for reaching said predetermined count is varied in accordance with said burst rate.

10. The telemetering system of claim 9, wherein said means for modifying said timer unit includes means for feeding said pulses corresponding to said burst rate to said timer counter.

11. The telemetering system of claim 10, wherein said means for discontinuing the feeding of further pulses to said accumulator comprises blanking means for disabling said clock pulse source.

12. The telemetering system of claim 11, further including display means responsive to the total number of pulses in said accumulator to display a digital representation of the physiological parameter of the transmitter signals being received.

13. The telemetering system of claim 7, further including phase lock means responsive to the output of said demodulator for producing a stable square wave pulse train having a repetition rate equal to the average repetition rate of said demodulator output.

14. The telemetering system of claim 7, wherein said means for measuring the burst rate of the received signals includes compensating means for correcting for nonlinearities in the burst rates of the signals generated by said transmitters.

15. The telemetering system of claim 14, wherein said compensating means utilizes the burst rate of the received signal for correcting for said nonlinearities.

16. In a system for measuring the burst rate of a train of bursts of radio frequency signals; a receiver tuned to receive such radio frequency signals; a demodulator operated by said receiver for producing a train of pulses at a frequency corresponding to the burst rate; pulse shaping means including a phase lock circuit adapted to sweep over a range of frequencies that overlaps the burst rate, said phase lock circuit being connected to receive the pulses developed by said demodulator whereby said phase lock circuit generates output pulses at a rate corresponding to said burst rate; measuring means responsive to said output pulses for producing a signal that depends on the burst rate of the received radio frequency signals.

17. A system as defined in claim 16 wherein said output pulses are rectangular and wherein said measuring means comprises a pulse counter and time-gated means for operating said pulse counter to measure the number of pulses applied to it in a predetermined time interval.

18. The system of claim 17, further including locking means responsive to the generation by said phase lock circuit of said output pulses to enable said measuring means, whereby said measuring means is capable of measuring said burst rate only when a phase lock exists between said output pulses and said pulses developed by said demodulator.

19. The system of claim 18, wherein said measuring means includes a timing counter; clock means for driving said counter; accumulator means; and first gate means controlled by said timing counter for applying said output pulses to said accumulator means over a period of time.

20. The system of claim 19 wherein said measuring means further includes second gate means controlled by said timing counter for applying said output pulses to drive said timing counter to vary said period of time in proportion to said burst rate.

21. The system of claim 20, wherein said measuring means further includes third gate means controlled by said timing counter for applying said output pulses to said timing counter over only a portion of said period of time.

22. The system of claim 21, wherein said measuring means further includes fourth gating means for applying to said accumulator means a fixed number of auxiliary pulses, whereby the total number of output pulses and auxiliary pulses applied to said accumulator means represents said burst rate.

23. In a teLemetering system for monitoring the variable physiological conditions of a plurality of living subjects that are spaced apart by a predetermined minimum distance, separate telemetering transmitters mounted on the respective subjects to generate carrier wave signals of about the same radio frequency with the carrier wave signals being emitted in bursts from each transmitter at an audio frequency that corresponds to the value of the physiological condition of the said respective subjects, said carrier wave signals having a length much greater than said minimum distance; the power of each transmitter being such that the signal-to-noise ratio thereof is less than 1 unit beyond said minimum distance; a single telemetering receiver for receiving carrier wave signals at the aforesaid radio frequencies simultaneously from a plurality of said transmitters; and means connected to said receiver for selectively generating pulses that correspond to bursts of the strongest of said carrier wave signals, and means responsive to said pulses for measuring said burst rate to indicate the physiological condition of the subject from which said strongest of said carrier wave signals is received.

24. The system of claim 23, wherein said means for selectively generating pulses comprises: a demodulator having an automatic gain control circuit for producing at its output detected pulses corresponding to the bursts of received radio frequency signals; and a phase lock unit responsive to said detected pulses for producing a stream of pulses at the output thereof at a rate corresponding to the burst rate of said received carrier wave signals, said phase lock unit including an oscillator and means for sweeping the frequency of oscillation from a high value above said burst rate to a low value below said burst rate, and means controlled by said detected pulses for locking the frequency of oscillation to the burst rate of said strongest of said carrier wave signals.

25. The system of claim 24, wherein said means responsive to said pulses for measuring said burst rate comprises: a timer unit; an accumulator; gate means controlled by said timer unit for feeding said stream of pulses to said accumulator for a predetermined period of time; starter means for initiating operation of said receiver, said accumulator, and said timer unit; means controlled by said starter means to initiate operation of said receiver unit and to delay the initiation of operation of said timer unit and said accumulator for a period of time sufficient to permit said phase lock unit to be locked with the received bursts of radio-frequency signals at said burst rate.

26. In a system for representing the value of a parameter that is a function of the pulse rate of a stream of input pulses which function is characterized by an intercept A at the 0 pulse rate, said system having input means for receiving such a stream of input pulses and a digital output counter for storing a manifestation of a total-number in digital form, the improvement that comprises: a timer unit including a clock pulse source, a timer counter, and means for feeding clock pulses from said clock pulse source to said timer counter; means controlled by said timer unit for gating input pulses during a first timer interval; auxiliary means for producing an auxiliary digital signal that is at least partially dependent on the value of said intercept A; means controlled by said gated pulses and by said auxiliary digital signal for storing in said output counter a manifestation of a total-number representing the value of said parameter.

27. In a system as defined in claim 26, a device for displaying numbers in visible form, and means controlled by received pulses for operating said device to display numbers stored in said output counter only when the total-number stored exceeds a predetermined amount.

28. The system of claim 27, wherein said timer unit includes a Clock pulse source, a timer counter for counting clock pulses from said clock pulse source and a decoder adapted to detect when the number of clock pulses counted has reached a value corresponding to the value of said parameter; starter means for initiating operation of said output counter, said time means, and said auxiliary means; and means controlled jointly by said decoder means and by said auxiliary means for storing in said digital output counter a manifestation of a total-number corresponding to the value of said parameter.

29. In a system for representing the value of a parameter that is a function of the pulse rate of a stream of pulses over a limited range of pulse rates and which function is characterized by an intercept A at 0 pulse rate, the improvement that comprises: an output counter for storing a total-number in digital form; auxiliary means for producing a set of digital signals that are at least partially dependent on the value of said intercept; input means for receiving such a stream of pulses; a timer unit, including a clock pulse source, and a timer counter; starter means for initiating operation of said output counter, said timer unit, and said auxiliary means; means controlled by said starter means for feeding pulses from said clock pulse source to said timer counter whereby a timing operation is initiated; means controlled by said starter means for feeding input pulses to said output counter; and means controlled by said timer unit when the number of clock pulses fed to the timer counter has reached a count corresponding to a determined time period for discontinuing the feeding of further input pulses to said output counter.

30. In a system for representing the value of a physiological parameter which involves the detection of the value of said parameter and the transmission of radio frequency signals from a transmitter in a stream of bursts at a burst rate that is a function of the detected value of the physiological parameter which function is characterized by an intercept A at 0 pulse rate: a radio-frequency receiver unit including means for receiving said bursts of radio-frequency signals and for converting the bursts of received signals into a stream of pulses that have a frequency proportional to the burst rate of said radio-frequency signals; means for producing an auxiliary digital signal representing a number corresponding to said intercept A; means for gating pulses in said stream during a selected time interval proportional to said burst rate; an output counter; and means controlled by said auxiliary digital signal and said gated pulses for storing in said output counter a digital manifestation of the sum of said numbers, thereby representing the value of said physiological parameter.

31. A system as defined in claim 30, said receiver unit including a demodulator having an automatic gain control circuit for producing at its output detected pulses corresponding to the bursts of received radio frequency signals; a phase lock unit responsive to said detected pulses for producing said stream of pulses at the output thereof, said phase lock unit including an oscillator and means for sweeping the frequency of oscillation from a high value above said burst rate to a low value below said burst rate, and means controlled by said detected pulses for locking the frequency of oscillation to the burst rate; starting means for initiating operation of said receiver unit, said output counter, said means for gating, and said means for producing an auxiliary digital signal; and means controlled by said starting means to delay the initiation of operation of said means for gating and said output counter for a period of time sufficient to permit said phase lock unit to be locked with the received bursts of radio frequency signals at said burst rate.

32. In a system as defined in claim 31, a device for visibly digital numbers in visible form; and means for operating said device to display the total number stored in said output counter only when the total number stored exceeds a predetermined amount.

33. A system for transmitting and receiving signals corresponding to a physiological parameter of a subject, comprising: a sensing element adapted to detect the value of said physiological parameter; a transmitter controlled by said sensing element to produce a modulated radio frequency magnetic field, said magnetic field being modulated in accordance with the value of the detected parameter; a receiver including antenna means for inductively receiving within the extreme-near-field region of said transmitter said modulated radio frequency magnetic field; electrostatic shield means for said antenna for reducing electrostatic radiation to and from said receiver without substantially reducing the reception of said magnetic field; phase lock means within said receiver and responsive to the modulation of said magnetic field for detecting the average rate of a repetitive component of said modulation and rejecting noise caused by interfering magnetic fields; and means responsive to said average rate for determining the value of said parameter.

34. The system of claim 33, wherein said means for determining the value of said parameter includes: means producing output pulses at said average rate; means accumulating a predetermined number of count pulses during a first time period and a variable number of count pulses during a second time period; and means responsive to said output pulses for varying said second time period in accordance with said average rate to compensate for nonlinearities in the relationship between said modulation and the value of said detected parameter, whereby the value of said parameter may be accurately determined by the total number of count pulses accumulated during said first and second time periods.

35. The system of claim 33, wherein said means for determining the value of said parameter includes counter means responsive to said average rate for producing count pulses at a rate which corresponds to said average rate, and accumulator means receiving and accumulating pulses produced at said average rate for a period of time defined by a predetermined number of said count pulses, said period of time varying in accordance with said average rate to compensate for nonlinearities in the relationship between the modulation of said transmitted magnetic field and the measured value of said parameter, whereby the value of said parameter is accurately determined.

36. The system of claim 33, wherein said transmitter includes antenna means for inductively transmitting said modulated radio frequency magnetic field, and electrostatic shield means for said transmitter antenna to reduce electrostatic radiation to and from said transmitter without substantially reducing the magnetic inductive transmission to the receiver.

37. The system of claim 36, wherein said transmitter antenna includes a tubular core of carbonyl iron and an antenna winding wound on said core, said transmitting antenna electrostatic shield encircling said winding and covering one end of said core.

38. The system of claim 36, wherein said transmitter comprises a blocking oscillator responsive to changes in said sensing element to emit bursts of radio frequency signals at a rate substantially propositional to said measured parameter, said means for determing the value of said parameter compensating for nonlinearities in the change of said burst rate with changes in said measured parameter.

39. A system for transmitting and receiving signals corresponding to a physiological parameter of a subject, comprising: sensing means responsive to the value of said parameter; transmitter means controlled by said sensing means for producing a varying magnetic field modulated in accordance with the value of said parameter; receiveR means responsive to said modulated magnetic field; means connected to said receiver means producing output pulses at a rate corresponding to a repetitive component of said modulated magnetic field; means accumulating said output pulses over a predetermined period of time; and means for varying said predetermined period of time in accordance with said rate to compensate for nonlinearities in the generation and transmission of said rate.

40. The system of claim 39, wherein said means producing output pulses includes means detecting the average rate of said repetitive component of said modulated magnetic field, whereby interfering magnetic fields are rejected by said receiver, and producing said output pulses at said average rate.

41. The system of claim 40, wherein said means for detecting the average rate of the repetitive component of a received modulated magnetic field comprises a phase lock circuit which locks onto, and thereafter generates output pulses at, a rate corresponding to the modulation of said magnetic field.

42. The system of claim 41, wherein said transmitted magnetic field is burst modulated at a rate which is substantially proportional to the value of said parameter, and wherein said output pulses are generated at a rate corresponding to the average rate of said burst modulation.

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